1. Field of the Invention
The present invention relates generally to an apparatus and method for sending a multicast packet in a mobile digital broadcast system, and in particular, to an apparatus and method for sending a multicast packet in a mobile digital broadcast system such that a broadcaster of the mobile digital broadcast sends the multicast packet and a receiver determines whether the multicast packet is a necessary packet by merely examining the header information.
2. Description of the Related Art
Digital Video Broadcasting-Handheld (DVB-H), which is a technology combining mobile and digital broadcastings, is rapidly spreading over Europe. The DVB-H broadcasts information to a user, such as Audio/Video (A/V) data, Entitlement Control Message (ECM), Entitlement Management Message (EMM), and Electronic Service Guide (ESG) data, by using an Internet Protocol Data Cast (IPDC) technique, which encapsulates the information in an IP packet.
DVB-H broadcasting basically works in a multicast manner to reduce the load of an irrelevant host because of the surge in broadcasting. The multicast technology sends a packet only to a host joining the group. How a general multicast packet is generated, transmitted, and received is described by referring to FIGS. 1 and 2.
FIG. 1 is a flowchart of a method for generating and sending a multicast packet at a general multicast transmitter in the prior art. When data to be multicast is generated in step 100, the general multicast transmitter of FIG. 1 inputs a multicast group address in a destination Internet Protocol (IP) address field of an IP header in step 102, completes the IP header generation in step 104, and multicasts a packet to a receiver by attaching data after the IP header in step 106.
FIG. 2 is a flowchart of a method for receiving and processing a multicast packet at a general multicast receiver in the prior art. Upon receiving a multicast packet in step 200, the multicast receiver of FIG. 2 determines whether the destination IP address of the IP header of the received packet matches a group address of the receiver in step 202.
When the two addresses match in step 202, the multicast receiver forwards a received multicast packet to an application program in step 204. By contrast, when the two addresses are different from each other in step 202, the multicast receiver discards the received multicast packet in step 206.
While a DVB-H system alleviates the load of the irrelevant host by operating in the multicast manner, there still exists a problem. To control the viewing authority for a scrambler channel of digital broadcasting channels, the DVB-H system employs a Conditional Access System (CAS) module. When a user purchases a scrambler channel using CALL/HTTP, the DVB-H system sends a UDP packet, being Entitlement Management Message (EMM), which contains a unique address and the purchased access authority of the corresponding user, to every receiver joining the multicast group. The receiver receives the EMM through a socket and forwards the EMM to its CAS. Upon receiving the EMM, the CAS determines whether the received EMM is destined for itself based on the ID information. When the received EMM is correctly received, the receiver uses the EMM to access the scrambler channel. When the received EMM is incorrectly received, the receiver discards the received EMM. The broadcaster of the DVB-H system sends the same EMM over a certain time period in the case where the EMM is incorrectly received at the receiver. In other words, when receiving the multicast packet containing the EMM, the receiver of the DVB-H system needs to forward the packet to the CAS being the application program and the CAS needs to determine whether the packet is necessary by comparing the ID information of the EMM as in step 204 of FIG. 2.
Thus, if 100,000 users purchase the access authority in that situation, the CAS of the receiver is subject to the unnecessary load while processing at least 99,999 EMMs, excluding one EMM corresponding to itself.